The invention pertains to navigational systems and specifically to an acoustical system capable of providing auditory information to a small boat operator regarding the relative location of a channel or the like when visual navigation is restricted.
Under conditions of fog or darkness, a small boat operator whose boat is not equipped with radar or other navigational systems is placed in danger under such circumstances and at the least becomes inconvenienced. Accordingly, when fog eliminates visual navigation, the small boat operator may attempt to find an anchor or tie-up point and wait for the fog to lift. Marker buoys serve as good temporary stopping points and these often have acoustic sources to assist in their location by simple directional listening through the fog. It would be more advantageous, however, for the boat operator to continue his course and proceed directly to the desired harbor or through the selected channel.
Although there are methods presently available for aiding in navigation near ports and harbor entrances when visual contact is lost, the small boat operator can hardly afford such expensive systems. Such systems include radar, distance measuring equipment and complicated charts and computers.
Therefore, it is an object of this invention to provide an inexpensive method for aiding a small boat operator in determining his location relative to a port or harbor entrance.
Another object of this invention is to provide a small boat operator with such information when visual conditions are so restricted as to prevent visual navigation.
It is a further object of this invention to provide a small boat operator with knowledge by simply listening to an anticipated sequence of directional sounds produced by an acoustic source.
And yet a further object of this invention is to provide a small boat operator with information regarding the location of a port or harbor entrance with respect to its own location without the introduction of an ambiguous component.
In addition to the above objects and advantages of this invention is a pair of fixed acoustic sources so positioned that both can be heard within a reasonable distance of a channel opening. Each acoustic source transmits a different tone on a narrow beam that sweeps across the water producing a sequence of pulses to a boat operator. The unaided human ear is able to decipher the tones in order to provide accurate information as to the exact bearing of the boat from the acoustic source. Moreover, the meterological conditions which are conducive to the formation of fog also includes favorable conditions for the propagation of acoustic signals. Specifically, the formation of fog often includes a stable movement of moisture laden tropical air into an area having relatively cold water. Radiation cooling also contributes to the creating of saturated air necessary for the formation of fog. Usually accompanied with the formation of fog is a low wind velocity. Therefore unless there is a significant noise level from wave action in surf, the background sound levels are low and favor the transmission and reception of the acoustic signal.